Graphene, a hexagonal honeycomb lattice shaped planar film comprising carbon atoms in an sp2 hybridized orbital, is a two-dimensional nanomaterial with a thickness of only one carbon atom, and a material most likely to trigger a new round of revolutions in the field of electronic technology.
With regard to graphene, it has the following features.
1) it is the thinnest but also the hardest nanomaterial in the world currently and is harder than diamonds, and its strength is 100 times higher than that of the best steel in the world;
2) it has excellent light transmission, is almost completely transparent, and only absorbs 2.3% of the light;
3) its greatest characteristic is that the movement speed of electrons therein reaches 1/300 of the speed of light, and far exceeds the movement speed of electrons in general conductors;
4) it is a material with the least resistivity in the world, the thermal conduction coefficient reaches up to 5300 W/m·K, and its electron mobility exceeds 15,000 cm2/(V·s) at ordinary temperature, while the resistivity is only about 10-6 Ω·cm; and
5) its structure is very stable, with the connection between each of carbon atoms being very flexible, and when an external mechanical force is applied, carbon atom planes will suffer from bending deformation, so that the carbon atoms are not required to be rearranged to adapt to the external force, thereby maintaining a stable structure, and enabling the carbon atoms to have excellent electrical conductivity.
Currently, common preparation methods of the graphene material are mechanical exfoliation method, chemical oxidation method, crystal epitaxial growth method, chemical vapor deposition method, organic synthesis method, carbon nanotube peeling method, etc. Samsung and Sungkyunkwan University are using the chemical vapor deposition (CVD) method, by which high-quality graphene can be prepared with a large surface area, but with a high cost and complex process.
With excellent features of hard texture, high transparency (transmittance≈97.7%), high thermal conductivity coefficient (up to 5300 W/(m·K)), high electron mobility (more than 15,000 cm2/(V·s)), and the like, graphene has been increasingly used in display devices in recent years, especially in touch screens (as an alternative to a conventional transparent conductive thin film ITO) and in the aspect of LED.
In recent years, due to the appearance of graphene light-emitting elements, applications of graphene in the display field are expanded. Display units made using a graphene material can change the light-emitting color of graphene light-emitting diodes by adjusting a gate voltage, and its principle is that the size of an electric field generated by the gate voltage can adjust the Fermi level of a semi-reduced graphene oxide, and therefore can adjust a light-emitting wavelength of graphene.
FIG. 2 is a schematic diagram of a display unit of a graphene display device prepared based on a semiconductor graphite oxide light-emitting material, and the display unit of the graphene display device includes an upper substrate, a lower substrate, and light-emitting structures, wherein the number of the light-emitting structures can be provided according to the specific requirements of the graphene display device. Each of the light-emitting structures comprises a light-emitting layer, a gate, a source, and a drain. The gate covers one side surface of the light-emitting layer towards the upper substrate, and the source and the drain are located on one side of the light-emitting layer away from the gate.
The light emitting layer of the display device is a semi-reduced graphene oxide. The source and the drain are a reduced graphene oxide, and the gate is a graphene oxide. One surface of the lower substrate of the display device facing away from the above mentioned structure has a high-reflectance metal reflecting layer. The material of the lower substrate can be a water-insulating oxide-insulating transparent organic material (PET), and can also be glass or nickel or the like, and the upper substrate is a water-insulating oxide-insulating organic material (PET) or glass or the like.
In terms of a graphene display device, the light-emitting layer can emit light with different colors according to differences of gate voltages. For example, when the gate voltage Vgs is between 0 V and 10 V and a source-drain voltage Vds is greater than a startup voltage Vth, graphene emits red light; when Vgs is between 20 V and 30 V and the source-drain voltage Vds is greater than the startup voltage Vth, graphene emits green light; and when Vgs is between 40 V and 50 V and the source-drain voltage Vds is greater than the startup voltage Vth, graphene emits blue light. The intensity of the emitted light can be changed by changing the size of the Vds voltage, and thereby a gray level can be adjusted.
Therefore, each of the light-emitting structures actually constitutes a dynamic pixel. Adjustment of the light emitting color of the light emitting structures can be achieved by controlling the source-drain voltage Vds, and each of the light-emitting structures can emit not only three primary colors of light: red, green, and blue (RGB), but also five primary colors of light: red, green, blue, yellow, and cyan (RGBYC), or even more colors of light. Therefore, a brighter and wider color gamut coverage can be realized; an aperture ratio of a display device can be increased; and the display power consumption can be reduced.
As graphene can use the same light-emitting material to achieve the different light emitting colors, the light emitting colors can be adjusted only by controlling the gate voltage. According to this principle, as few pixel units as possible can be used to achieve a brighter and wider color gamut coverage and a lower power consumption, and to improve the display device aperture ratio.
By utilizing the unique light-emitting characteristic of graphene, traditional RGB 3-primary color pixels are designed into three dynamic sub-pixels, so that a graphene display device that uses only three sub-pixels can achieve the purpose of RGBYC (red-green-blue-yellow-cyan) 5-primary color display; and so-called DDD is dynamic pixels, wherein the selection of dynamic pixel colors is determined by an input RGB signal.
The graphene display device can achieve, by using a drive design of dynamic pixels, RGBYC 5-primary color high color saturation display which can be hardly achieved through traditional LCD display devices. To achieve, with three dynamic sub-pixels of the graphene display device, RGBYC 5-primary color based ultra-wide color gamut display, a pixel color gamut covered by RGBYC is required to be divided, and then three different pixels are selected according to the positions where the colors are located.
As shown in FIG. 3, with a current five color patch dividing method as an example, in a rectangular plane coordinate system, the color gamut where RGBYC is located can be divided into five triangular color patches of WBR, WCB, WGC, WYG, and WRY, the triangular color patches have a predetermined matching relationship with display colors of the dynamic sub-pixels, and each of the triangular color patches has corresponding display colors of the dynamic sub-pixels. The position of a pixel in the pixel color gamut can be determined according to an input pixel chromaticity coordinate A (x, y), and the display colors of three dynamic sub-pixels can be determined according to the position of a pixel in the pixel color gamut. FIG. 4 is a diagram of the correspondence of the position of a pixel chromaticity coordinate A (x, y) and the display color of the dynamic sub-pixel.
The gray levels of the dynamic sub-pixels are determined according to input gray level values RiGiBi of an RGB pixel, and the value of i is in the range from 0 to 255, which represents the gray level value. However, it cannot be guaranteed that when A (x, y) is in any one of the triangular color patches, and the input gray level value signals of an RGB 3-color signal are close to the same, the output luminance is substantially close to the white color chromaticity. That is to say, the consistency of the color coordinates of white points is poor.